The use of electric heating elements, including electric ranges, hot plates, and the like, is pervasive throughout most modern kitchens. In such heating systems, electric current is used for the resistive heating of a wire that may be encased in a helical heating element or otherwise encased in a thermal unit as a flat heat source. One problem attendant with such heating elements, though, are localized heating phenomena or "hot spots" that occur over the support surface of the heating element. Since a cooking vessel placed on the heating element is primarily heated by thermal conduction along the base of the cooking vessel, it is not unusual for the base of the cooking vessel to have corresponding hot spots of greater temperature even though the average temperature over the base is much lower. Food or beverages which are placed in the vessel and which are heated by the heating element may accordingly become scorched or burned by these localized hot spots.
One particular type of apparatus to which the present invention is specifically directed is hot beverage brewing devices of the drip brew type, especially drip brew coffee makers. This industry encompasses both multiple unit commercial coffee makers used, for example, in restaurants and institutional kitchens, and single unit home drip brew coffee makers such as those currently marketed by a wide variety of manufacturers. This industry is of particular interest since there has been a rapid expansion of use of coffee makers in the home, as well as in restaurants, over the last 20 years. These coffee makers have, to a large extent, replaced percolating coffee pots both electric and non-electric.
As is well known, the typical coffee maker includes a housing and boiling unit which receives water and heats the water to a brewing temperature. This water is conveyed and dispensed through a coffee-holding filter assembly wherein the water becomes flavored by the coffee and is downwardly dispensed under gravity into a receiving vessel, preferably in the form of a glass coffee pot. This coffee pot receives and stores the brewed coffee from the coffee maker and traditionally rests on a heating element or hot plate thermostatically controlled by the coffee maker. These hot plates may either be a constant temperature heat source, normally in the range of 220.degree.-250.degree. F. or, in the alternative, are cyclical between an "on" state and an "off" state whereby the coffee remains at a fairly constant temperature. In the cyclical systems, though, the heat source typically has a peak amplitude of maximum temperature in the "on" state that exceeds 250.degree. F. to compensate for those times when the source is inactive.
Due to localized heating of both the steady temperature and the cyclical heating elements, excess temperatures at localized areas are transmitted by thermal conduction to that portion of the beverage adjacent thereto. This transmission of excessive heat causes a cooking action within coffee which degenerates flavorable attributes, such as flavor, aroma, and color. Over a period of time, an increasing portion of the coffee is exposed to the excess temperatures, with this situation only being compounded by the removal of coffee for consumption. Therefore, the stored coffee in the coffee pot becomes increasingly degraded over time.